The present invention relates to acidic treatment fluids used in industrial and/or subterranean operations, and more particularly, to acidic treatment fluids comprising clarified xanthan gelling agents, and methods of use in industrial and/or subterranean operations.
Acidizing and fracturing procedures using acidic treatment fluids are commonly carried out in subterranean well formations to accomplish a number of purposes including, but not limited to, to facilitate the recovery of desirable hydrocarbons from the formation. As used herein, the term “treatment fluid” refers to any fluid that may be used in a subterranean application in conjunction with a desired function and/or for a desired purpose. The term “treatment fluid” does not imply any particular action by the fluid or any component thereof.
One commonly used aqueous acidic treatment fluid comprises hydrochloric acid. Other commonly used acids for acidic treatment fluids include hydrofluoric acid, acetic acid, formic acid, citric acid, ethylene diamine tetra acetic acid (“EDTA”), glycolic acid, sulfamic acid, and derivatives or combinations thereof.
Acidic treatment fluids are used in various subterranean operations. For example, formation acidizing or “acidizing” is a method for, among other purposes, increasing the flow of desirable hydrocarbons from a subterranean formation. In a matrix acidizing procedure, an aqueous acidic treatment fluid is introduced into a subterranean formation via a well bore therein under pressure so that the acidic treatment fluid flows into the pore spaces of the formation and reacts with (e.g., dissolves) the acid-soluble materials therein. As a result, the pore spaces of that portion of the formation are enlarged, and the permeability of the formation may increase. The flow of hydrocarbons from the formation therefore may be increased because of the increase in formation conductivity caused, inter alia, by dissolution of the formation material. In fracture acidizing procedures, one or more fractures are produced in the formation(s) and an acidic treatment fluid is introduced into the fracture(s) to etch flow channels therein. Acidic treatment fluids also may be used to clean out well bores to facilitate the flow of desirable hydrocarbons. Other acidic treatment fluids may be used in diversion processes and well bore clean-out processes. A specific example is filter cake removal.
To increase the viscosity of an aqueous acidic treatment fluid, a suitable gelling agent may be included in the treatment fluid (often referred to as “gelling” the fluid). Gelling an aqueous acidic treatment fluid may be useful, among other purposes, to prevent the acid from becoming prematurely spent and inactive. Additionally, gelling an aqueous acidic treatment fluid may enable the development of wider fractures so that the gelled acidic treatment fluid may delay the interaction of the acid with an acid soluble component in the well bore or the formation. Moreover, gelling an aqueous acidic treatment fluid may permit better fluid loss control.
Acidic treatment fluids used in subterranean operations are predominantly water-based fluids that comprise gelling agents that may increase their viscosities. These gelling agents are usually biopolymers or synthetic polymers that, when hydrated and at a sufficient concentration, are capable of forming a more viscous fluid. Common gelling agents include polysaccharides (such as xanthan), synthetic polymers (such as polyacrylamide), and surfactant gel systems.
Acidic treatment fluids comprising xanthan generally have sufficient viscosity for lower temperature operations. At elevated temperatures (e.g., those above about 120° F. to about 150° F.), however, the viscosity of such xanthan treatment fluids sometimes is diminished. Consequently, xanthan may not be a suitable gelling agent for acidic treatment fluids when those fluids are used in subterranean formations that comprise elevated temperatures. Other gelling agents such as synthetic gelling agents (e.g., polyacrylamides) have been used in subterranean formations at these elevated temperatures, but often they are difficult to disperse and usually require considerable mixing or agitation to develop full viscosity. Additionally, most conventional gelling agents, including guar and some synthetic polymers, may form acid-insoluble residues. Surfactant gel systems also have been used in subterranean formations at these temperatures, but such systems can be expensive, can be sensitive to impurities, and may require hydrocarbon breakers.